Semiconductor devices are typically packaged within a molded body for protection against the corrosive elements of the environment. With one type of package, the semiconductor device is coupled to an associated circuit by a plurality of parallel conductors or leads which project from the molded body. The parallel leads typically are positioned on two or four sides of the molded package. The leads are constructed from a pliable metal which can be easily formed into a desired configuration without damaging either the semiconductor chip or the molded body. However, the application of even a small amount of pressure may bend the leads away from the desired shape and position. The deformed leads of a semiconductor device may be pressed close together, removing the pre-formed parallelism, or bent vertically relative to the molded body so that they do not lie on a common plane. Pre-formed bends in the lead connectors may be distorted. The lead conductors on opposing ends of the molded body may be bent, distorting the tweeze or tip-to-tip distance of the device. Once out of position, the leads may not match with the pads on the associated circuit board and the semiconductor package will be considered to be defective. Even when considerable care is taken while handling the packaged semiconductor device, the leads of a large number of semiconductor devices may be bent away from the predetermined configuration.
One method of mounting a semiconductor device to a circuit board is accomplished by positioning the device on the board by hand and then manually soldering it in place. Another application method is to use an automatic placement machine to set the device on the circuit board, and then apply heat to the board to melt the solder paste beneath the leads. For the automatic placement method, leads which are out of shape and/or position may not rest on a spot of solder paste such that no connection is made with the associated circuit.
Methods exist in the art for salvaging some of the defective semiconductor devices by straightening the bent leads. The bent lead conductors can be reformed by manually bending each lead back to the appropriate configuration. However, this process is extremely time consuming and subject to human error. If the leads are not severely deformed, they may be reformed by spanking the semiconductor device or compressing the leads between opposing dies. However, compressing the lead conductors will not reintroduce parallelism between the leads. U.S. Pat. No. 4,727,912 shows a device in which one of the dies is formed with teeth. Although this device may reintroduce parallelism between some of the less deformed leads, other leads may be damaged by the teeth on the dies. A system for reconditioning bent leads into a parallel and predetermined shape is desirable.
Another method for conditioning the deformed leads uses opposing blades to straighten and massage the leads as the semiconductor device passes along a track, as is disclosed in U.S. Pat. No. 4,481,984. Reforming the leads using these opposing blades may not be effective for severely bent leads. Moreover, the system may only be used with packages having leads positioned on two opposite sides of the device. A system which may be used to efficiently recondition leads projecting from four sides of a semiconductor device is desirable.
U.S. Pat. Nos. 5,273,081 and 5,487,416 disclose multi-stage conditioning systems in which the leads are massaged at a first station to reintroduce parallelism and then moved to a second station where dies form the leads to remove elastic memory from the leads. The third station reforms the leads to the predetermined configuration.
The actual dimensions of the molded package vary from manufacturer to manufacturer. Because of the precision required to reform the leads to the exact predetermined configuration, dimensional variations may impair the ability of a conditioning system to simultaneously reform all of the leads. Prior to conditioning the leads, a sample package from each batch must be carefully measured and adjustments made to the conditioning system to accommodate the size variations. These adjustments typically require partially dismantling and then reassembling the machinery. A lead conditioning system in which the leads are scanned and the conditioning system is automatically adjusted to accommodate different semiconductor packages as well as different lead configurations is desirable.